Thickened inorganic nitrate aqueous slurry containing finely divided aluminum having a lyophobic surface of high surface area



United States Patent Office 3,367,805 Patented Feb. 6, 1968 THICKENED INORGANIC NITRATE AQUEOUS SLURRY CONTAINING FINELY DIVIDED ALU- MINUM HAVING A LYOPHOBTC SURFACE OF HiGH SURFAtJE AREA Robert B. Clay, Bountiful, and Lex L. Udy and Donald T. Bailey, Salt Lake City, Utah, assignors to Intermountain Research and Engineering Company, a corporation of Utah No Drawing. {lontinuation-in-part of application Ser. No. 301,630, Aug. 12, 1963. This application June 2, 1965, Ser. No. 460,857

17 Claims. (Cl. 1496) This application is a continuationdn'part of Ser. No. 301,630, filed Aug. 12, 1963, now abandoned.

The present invention relates to an improvement in gel or slurry type blasting agents. It has particular application to plastic aqueous slurired or gel type blasting agents which are composed in large part of ammonium nitrate and which are suitable for various uses but are particularly useful in blasting hard rock. Due to their plastic fluid or semifluid nature, they can be pumped through pipes or hoses and can be placed in boreholes and in other comparable sites and fill the hole or site completely for more effective and etficient operation than some of the prior art solid blasting compositions.

As is Well known, blasting agents of plastic or fiowable type have been prepared in the past by blending an aqueous solution of ammonium nitrate with other materials. including particulate aluminum, with or Without other sensitizers and the like. The present invention relates to compositions of this same general type but involves improvements particularly in respect to the sensitivity, the efiiciency, power output, etc., of the explosive slurry.

As disclosed, for example, in US. Patent No. 2,930,685 and Reissue No. 25,695 to Cook and Farnam, a blasting composition of the slurry type containing relatively large proportions of ammonium nitrate and enough water to make them mobile or flowable, have been prepared in the past. In Patent No. 2,930,685 a particulate or trinitro toluene (TNT) is described as a preferred sensitizer, but other materials including aluminum are mentioned. In Reissue No. 25,695 particulate aluminum is used as the preferred or primary sensitizer. The present invention also makes use of aluminum for the same purpose.

In addition to the use of sensitizers such as TNT and/ or aluminum, the prior art also has suggested the use of fuels added to the ammonium (or ammonium plus sodium) nitrate, such as hydrocarbons, sugars, starches and the like. The present invention likewise contemplates the use of such fuel materials when they are desired.

A number of suggestions have been made in'the prior art, also, regarding use of finely divided metals to contribute energy to the explosive. In particular it has been suggested that particulate aluminum, as well as other metals, might be used for such purposes. The prior art 'has proposed the use of various metals of high thermal energy, including aluminum, magnesium, boron and the like. These metals are used both as fuels and as sensitizers. In general, however, these materials when used have been employed predominantly as fuels. They have also been used normally in rather substantial proportions; for example, the prior art has suggested that finely divided aluminum be used in proportions of percent or more and even as much as 40 percent or more by Weight of the total composition. Such quantities of the really satisfactory metals are quite expensive. Moreover, they are not particularly effective in many cases.

According to the present invention, the proportions of the finely divided metal, and aluminum is the metal specifically preferred, which are to be used, are relatively much less than commonly suggested for employment in the prior art. The reason for this is that, according to the present invention, the metal is employed primarily as a sensitizer and is of a particular character for its special purpose. It is not used significantly as a fuel because the proportions employed are so minor, relatively speaking. Their contribution to the fuel energy is generally quite unimportant, although it may be somewhat significant in some cases.

An important aspect of this invention, then, is the use not only of relatively very small proportions of aluminum but its use in the most appropriate forms to accomplish proper sensitization of the inorganic nitrate based explosive composition. This requires that the aluminum employed be in such a form as to have very high sensitizing activity under explosion conditions. It promotes the detonation of the blasting agent to an unexpectedly high degree. In turn, this requires for one characteristic a high surface area; that is, an area of at least 0.5 square meter (5,000 square centimeters) per gram. Preferably, the finely divided aluminum is very fine grained, i.e., it has a surface area of a square meter or more per gram. Aluminum powders passing a 400 mesh sieve, or, in general, those especially prepared so as to have surface areas up to 2.5 and as much as 10 or more square meters per gram are particularly useful.

For another characteristic the metal must have surface active properties, or Wet-resistance, such as to promote the propagation of explosion to an unusually high degree. This will be further explained below.

By inorganic nitrate based explosive, it is intended to cover compositions based largely on ammonium nitrate which also may include other inorganic nitrates such as sodium nitrate. For purposes of this invention, ammonium nitrate will generally comprise at least 50% and usually or more of the total inorganic nitrate content. The inorganic nitrates, on the whole, Will comprise at least 40% by Weight and usually 50% or more of the total gel or slurry blasting composition.

Whereas the prior art has suggested in general terms the specific use of finely divided aluminum and other metal powders, it has now been found, quite unexpectedly, that aluminum having particular properties of surface area and of surface activity such as to establish reaction sites in great numbers may be employed in much smaller proportions than hitherto considered useful and with very important effects. When so employed in slurry type explosive compositions, of the type already mentioned, and to be explained in greater detail presently, very effective and powerful sensitization for blasting purposes is realized. This is accomplished by the use of relatively very low and therefore very inexpensive quantities of metallic aluminum.

While effective sensitization is desired, an overactive composition, i.e., having storage instability because of reactvity of the metal with other ingredients, such as the Water in the slurry, must be and is avoided in the present invention. This is accomplished by proper choice of the metal and, of course, by proper compounding.

In general terms, then, the invention contemplates a composition which contains as its principal and essential ingredients ammonium nitrate (or a combination of ammonium and sodium nitrate, etc.), water, or a watercontaining liquid, preferably a small amount of a thickener to prevent undue water extraction or water intrusion in dry or Wet boreholes, respectively, and relatively very small proportions of the particulate aluminum. The latter, as noted above, must be in such a form as to give a very effective sensitization effect to the explosive although the quantity used may be quite minor.

In its preferred form, then, the composition of this invention is a flowable slurry, having the typically consistency of wet plaster or concrete. It may be more or less fluid but is at least a plastic or so-called stick-type slurry of good explosive properties. It usually contains enough liquid to make it flow. The explosive properties include a proper degree of sensitivity for practical and effective detonation by means of boosters of reasonable size. The compositions must have adequate power for effective blasting and must detonate completely. For space efficiency they preferably have relatively high density. The density of the slurry as pumped or poured into a borehole, for example, is preferably above about 1.3 as compared with water in most cases. In some cases it may be slightly lower, down to 1.2. Density may be as high as 1.5, or more, and even as high as 2.0 in particu- "larly preferred compositions, especially those which are used for pumping into large boreholes and other cavities where explosive is to be used in mass.

The composition of this invention also is reasonably well oxygen balanced, preferably at least within limits of :10 percent and more preferably within limits of about :5 percent. Instead of prior art sensitizers used in relatively large proportions, relatively small amounts of the active aluminum are used. In fact, the aluminum as used may be so reactive with the water contained in the slurry as to require an inhibitor, particularly when the composition is to be held in storage for any appreciable length of time. Experience has shown that compositions of this type which contain aluminum of the desired degree of activity, when compounded without inhibitor, may heat up spontaneously within a few days or hours in storage at ordinary ambient summer temperatures. Suitable inhibitors are disclosed in US. Patent No. 3,113,059. Hence, the invention contemplates the use of a particularly effective aluminum sensitizer in combination with a suitable inhibitor which will protect the aluminum from attack by the water of the slurry while in storage. The stabilizer, of course, must not prevent effective sensitization by the aluminum.

When storage periods are very short as, for example, when the composition is mixed and immediately placed in the borehole for use, the inhibition of the aluminumwater reaction may be unnecessary. Under conditions invovlving storage, it is more essential. Water repellent aluminum is of course relatively inert.

Further, according to the present invention, the wet pourable or plastic slurry or gel compositions preferably contain'a thickening agent. This agent preferably is such that it will not set up sufficiently to interfere seriously with flow of the composition, e.g., in pumping it through hoses or pipes into boreholes, for example, but which, when the explosive is in place, will increase its viscosity and/or water resistance enough to effectively inhibit or prevent substantial extraction of the water from the slurry when the composition is placed in contact with a dry or porous formation. If the borehole or other blasting site contains water the thickener will prevent or at least effectively inhibit syneresis or leaching, or dilution.

Thus, the slurry compositions of the present invention are preferably thickened with an agent such as guar gum, or a flour, or a starch, or a combination of such materials. Enough thicknener preferably is used to set the gel or slurry up to a relatively stiff or viscous consistency which will resist the extraction of water from or intrusion of extraneous water into the plastic mass, prior to detonation. Excessive water extraction or dilution or leaching impair the blasting power of the explosive.

The gels or slurries of this invention preferably have the very convenient property of being quite fluid when first formed and hence readily pumpable as liquids for injection into boreholes. For this reason, the thickener desirably is one which is not effective immediately but which when the blasting agent is in place'will cause it to set up quickly and firmly within the formation. This not only inhibits water intrusion and extraction or syneresis .but also inhibits gravity separation of suspended solid particles, particularly particles of aluminum and of undissolved nitrate, etc., Which otherwise might occur while the gel or slurry is standing prior to being detonated.

Thus the invention contemplates as a preferred material an explosive blasting composition which, while containing as its principal essential ingredients ammonium nitrate, water and relatively very small but adequate proportions for sensitization of highly active aluminum, also has good fluid properties for'injection into a blasting site, e.g., a borehole, accompanied by setting up properties as it becomes quiescent in situ. In its preferred form the invention includes the use of supplementary materials including the inhibitor agents previously mentioned, thickener materials just discussed, and fuels or other sensitizers or modifiers. These may greatly improve the characteristics of the explosive composition. A simple composition made only of ammonium nitrate, water and aluminum, while effective as an explosive, may not bewell balanced, in regard to oxygen content. A superior and more powerful explosive may be made by incorporating, in addition to the ingredients named, a fuel material which will improve the oxygen balance. The latter material may be selected from numerous fuels including liquid, plastic and solid hydrocarbons or hydrocarbon derivatives such as glycols, alcohols, ethers, etc., carbonaceous and hydrocarbonaceous materials in general, such as coal, gilsonite, etc., or certain carbohydrates, e.g., starch, sugar, or concentrated sugar solutions. An excellent example of an effective sugar solution is molasses. A typical molasses contains about carbohydrates and about 20% water, as an example.

As a thickening agent a small amount of the agent known commercially as guar gum may be used. Alternatively, a carbohydrate material which has more fuel value than guar gum as well as having reasonably good thickening properties, may be employed. Starch, which term also may include flour generally, is preferably precooked to enhance its thickening power when used; such is very satisfactory, although a less effective thickener on a quantity basis than guar gum. Alternatively, starch and guar gum may both be used, if desired. By thickening the explosive plastic composition with such thickeners, a suitable composition is obtained for placing in the borehole by pumping. At the same time the composition becomes reasonably proof against undue water extraction, due to contact with dry, porous surfaces in the formation.

It is also highly desirable, as mentioned above, that compositions of this general type be as dense as reasonably possible for optimum blasting potency, bearing in mind the fact that sensitivity usually decreases with increase of density. The prior art has previously suggested that solid particulate ammonium nitrate may be included in a saturated aqueous solution of ammonium nitrate. Density may be increased over that of the normal ammonium nitrate-Water slurry composition by incorporating additional soluble or partly soluble materials such as dense oxygen donor salts of which sodium nitrate is a good example. Supplementary materials may be added for further improving sensitivity such as sulfur. Some ammonium nitrate based compositions containing sulfur and sodium nitrate are found to be somewhat more sensitive than those related materials which do not contain them. By means of such the amount of the sensitizing aluminum required may be further reduced. In compositions designed for use in large diameter boreholes or in large masses the aluminum content may be reduced to a level as low as about 0.1% or even 0.05% by weight based on the total composition.

Not only is an inhibitor useful to prevent substantial premature chemical reaction between the active aluminum and the water as explained above but a carefully chosen inhibitor may also prevent or assist in preventing syneresis and hence stabilize the composition physically. Inhibitors such as those disclosed and claimed in US. Patent No.

3,113,059 have this property. Ammonium or alkali metal phosphates and phosphites are particularly suitable. Other things being equal, it appears that the more finely divided the aluminum, or the greater its surface area, the more effective will be its sensitization activity. Of course, with increasing sensitization activity, the aluminum also becomes more reactive with the water, and indeed more reactive with oxygen from any source. Inhibitors therefore tend to be more essential with finer grades of aluminum.

The amount of aluminum sensitizer and its effectiveness for the purposes of the present invention vary considerably with its exact nature. In general terms, for the so-called large critical diameter explosives, i.e., those having a critical diameter of as much as about 5 inches 3 or greater, the amount of sensitizer required may be relatively very small. Typical compositions of this character may be quite effectively sensitized with proportions of finely divided aluminum as low as about 0.1% or less. Quantities of aluminum required, if it has the desired properties, ordinarily will not exceed about 0.5%, in large diameter columns. These properties or characteristics will next be discussed.

It appears that successful detonation of a gel or slurry type explosive depends on the establishment of a very large number of detonation or propagation sites well distributed throughout the explosive mass. By use of a finely divided aluminum well dispersed, these sites or reaction centers, as they may also be considered, are situated near enough together, throughout the mass, that they can greatly facilitate the detonation wave. It appears that tiny voids, free of liquid and in direct contact with the aluminum particles, are the effective reaction centers. Hence the aluminum particles not only must be of small size but they should not be completely wet by the water or other liquid of the slurry. Particulate aluminum which is somewhat liquid repellant or lyophobic, and of surface area of 0.5 to square meters per gram, preferably 1 to 5 square meters, is therefore preferred. Paint grade aluminum powders have such properties and are commercially available. They may be further improved by ball milling or by rolling the commercial powder between steel rollers to increase surface area and sensitization activity.

In general, quantitative requirements for aluminum appear to be somewhat inverse to water content, within appropriate limits. For a pumpable slurry or gel to be used in large boreholes, with 11 to water content, or, more broadly, above 6 or 7 percent liquid content, minimum or near minimum quantities of finely divided aluminum (e.g., 2.5 square meters per gram) will suffice, e.g., 0.1 to 0.2% by weight. For a relatively dry stick slurry, of slender column diameter (below about 2 inches) with water content of about 7 to 10%, the aluminum requirements may increase to as much as 1.2. In extreme cases 5% by weight of aluminum may be used. This may be generalized somewhat by stating that in many slurry explosives of ammonium nitrate base the total weight proportions of water and finely divided aluminum will generally lie between about 10 and 15 to Y percent, preferably about 12 to 15%, in many cases. Thus, with 15% water, for a five inch borehole or layer, 0.1% aluminum (of at least 0.5 m. area per gram) will suffice if it has liquid repellant active-site'forming properties. With'a very dry slurry, of about 8% water content, 2 to 3 and even 5% of the same aluminum is desirable. However, excellent slurries or gels can be made which contain more or less water.

The proportions of inhibitor should increase as alumi mum is increased, especially in the very fine particle size grades, butprefera bly at about the square root rate of the percentage of aluminum increase.

The so-called stick slurry compositions which are almost solid and are often useful to replace stick dynamite and similar prepackaged explosives are usually made and wrapped in stick sizes, e.g., of less than about 2 inches maximum diameter. As in the case of plastic slurries for injection in slender boreholes, the proportions of aluminum with high activity /2 to 10 square meters surface area per gram and wet-resistant surface) should be increased to 1% or substantially more in some cases.

The invention will be more fully understood by reference to specific examples.

EXAMPLE 1 A composition is prepared consisting of the following proportions by weight of the ingredients named: 78.5% ammonium nitrate, 15 water, 1.0% finely divided paint grade aluminum with a water repellant surface of at least 0.5 meter surface area per gram, 5% gilsonite and 0.5% guar gum. This material is an effective explosive and has a satisfactory propagation rate in boreholes of 4 inches diameter or greater. A high brisance booster of modest size is adequate for complete detonation.

EXAMPLE 2 A composition somewhat similar to that of Example 1 is prepared of the following ingredients in the proportions stated, by weight: 73.5% ammonium nitrate, 10% water, 0.5 finely divided aluminum (paint grade, average particle diameter about one micron and having a water repellant surface), 15% molasses of about 20% water content and 1% guar gum. This composition is in reasonable oxygen balance (within i10%) and contains an effective concentration of about 13% water. It is a plastic, smooth flowing solid and it gives excellent propagation properties in boreholes of 4 inches diameter or larger. However, it is not fully stable in storage and needs an inhibitor when storage over any extended period of time is contemplated.

EXAMPLE 3 This composition consists of the following ingredients, in the weight proportions indicated: 61.5 ammonium nitrate, 10% water, 0.5% aluminum (paint grade of about one micron average particle diameter and of somewhat water repellant character), 15 molasses of about 20% water content, 1% guar gum, 10% sodium nitrate and 2% sulfur. This product is somewhat more dense than that of Example 2 although generally similar in overall characteristics. It has a specific gravity of about 1.3 grams per cc. Due to the inclusion of sodium nitrate and sulfur it is somewhat more sensitive when cold and somewhat less sensitive, relatively speaking, when hot than the composition of Example 2. This property of sulfur-sodium nitrate gel or slurry is desirable for explosives used all year around.

In Examples 2 and 3 the proportions of aluminum may be reduced to as little as 0.2% with a corresponding slight increase in ammonium nitrate composition and still perform satisfactorily. Due to the fact that the composition of Example 3 includes sodium nitrate and sulfur, the proportions of aluminum required may be further reduced for use in large boreholes. Proportions as low as 0.2% are adequate for four inch boreholes and for holes of five or six inches or larger diameter, aluminum content can be further reduced to as low as 0.1% by weight without substantial loss of sensitivity or propagation characteristics. These low aluminum content blasting materials are particularly satisfactory for large explosions involving boreholes of five inches diameter or greater. With proportions of 0.5 of highly active aluminum they are satis'factory not only for the larger boreholes but also for intermediate and smaller bores, down to as smallas about two inches diameter. At the same time they are not so sensitive as to be hazardous.

EXAMPLE 4 A further composition is made up of generally similar proportions to those of Example 3, except that minor proportions of additional fuels such as carbonaceous materials, hydrocarbons and/ or carbohydrates are added, along with an inhibitor to prevent premature or rapid reaction of the finely divided aluminum with the water. The weight proportions of a specific composition of this Example are as follows: 60% ammonium nitrate, 10% sodium nitrate, 2% sulfur, 15% Water, 0.2% Water repellant aluminum (of 0.1 micron particle size average diameter indicating a surface area of about 6 to 7 square meters per gram), 1% guar, 1% starch, 2% finely divided gilsonite (a native asphaltic mineral, largely hydrocarbonaceous), 6% molasses as in Example 2, and 0.2% of a phosphoruscontaining inhibitor.

When guar gum is used as the sole thickener, proportions preferred are between about 0.2 and 2% by weight. Usually 0.5 to 1% is used. In lieu of the guar gum in any of the above examples, starch may be used. However, more starch generally is required than guar gum to obtain an equivalent thickening effect. For example, about 3% of common potato starch or wheat flour is equal to about 1% of guar gum in thickening power, provided the starch is precooked. Hence 0.6 to 6% of starch should be used if starch is the sole thicknener, or lesser proportions along with some gua'r gum. If not precooked, starch is often a rather inadequate thickener, especially where the explosive is used or stored at low temperatures. All of the above mentioned thickeners have the advantage, however, that in addition to giving thickening action they have a definite fuel value. As previously mentioned, adequate thickening of the slurry type explosive composition, with final thickening preferably occurring after the composition is placed in the borehole, is very desirable.

While paint grade aluminum has been mentioned in Examples 1 to 4, another procedure which has been found particularly effective is to grind or comminute very thin films or foi'ls of sheet aluminum which have, or may be treated to have, lyopho'bic surfaces. The granular material thus obtained has relatively very large surface areas per unit of weight, due probably to the numerous microscopic surface folds and convolutions. 'It therefore provides a vast number of reaction centers, well distributed throughout the blasting agent. Depending on quantities used, aluminum powders having a grain size which passes a 100 mesh sieve may be reasonably satisfactory if they have proper surface active properties. They are more satisfactory, however, and can be used in smaller quantities, if they are sufficient'ly fine to pass a finer, e.g., a 400 mesh sieve. Materials of the latter type generally will have a surface area of 25,000 square centimeters per gram or more.

EXAMPLE 5 Highly active aluminum is used as a sensitizer in essentially the same proportions and effectiveness as in Example 4.

EXAMPLE 6 A particularly effective particulate aluminum for purposes of this invention is a paint grade material passing through a 400 mesh screen and which has been contacted or coated with powdered stearic acid to render its surface highly water repellant. A composition of the following formula is a very effective blasting agent, Proportions are by weight.

Ammonium Nitrate 38.0 Sodium Nitrate 15.0

Water 17.0 Phosphate stabilizer 0.1 Aluminum 1.1

Sulfur 6.0

Gilsonite s 4.0

Guar-gum 1.1

Particulate ammonium nitrate 17.7

The first three ingredients are combined to make a liquid solution and the others are added and blended into the mixture cold. The liquid may be heated moderately, if desired.

In general, inorganic nitrates are used in greater proportions than will remain in solution in field blasting conditions. Most of the other ingredients are either insoluble or marginally soluble; hence the slurry or gel is an aqueous suspension, For part of the water other liquids such as glycols, alcohols, etc. may be added and ingredients not listed but known in the art to be useful may be incorporated without departing from the spirit of the invention.

In addition to the fine aluminum with hydrophobic or, more broadly, lyophobic properties, a coarser particled metal may be used and it may be coated to make it water repellant or not, as desired. As a rule, coated metal is preferred and combinations of 0.1% or even 0.05% of the paint grade metal plus 1% or more up to 10% or more of a coated coarser product such as ground foil, etc., is a very effective sensitizer. If desired, other metals which contribute fuel value, such as particulate magnesium, can be used along with the fine active aluminum in similar proportions.

In summary, the invention is a slurry or gel-type explosive composition, either pumpable or at least plastic in nature, which contains a relatively small but highly effective amount, about 0.05 to 5% by weight, of a finely divided, surface active aluminum capable of establishing avast number of void reaction centers well distributed throughout the explosive mass. The composition desirably iucludes 0.1 to 20% of a fuel of carbonaceous, hydrocarbon or carbohydrate type such as finely divided coal, gilsonite, flour or sugar. Molasses is a fuel which contributes substantial fuel value, imparts plasticity, and has desirable thixotripic properties. It is a suitable additive. The ammonium nitrate content maybe partly but not entirely replaced with sodium nitrate. When sodium nitrate is used, sulfur is desirably used too. A thickener which does not immediately interfere too much with fluidity or pumpability but which sets up quickly and effectively after a short time, especially after placement in a borehole, is a further important and desirable feature. Also, as has been indicated, it is desirable to include 0.02 to 2% of a phosphorus-containing inhibitor for the aluminum-water reaction, which inhibitor also preferably helps, along With the thickening agent, to prevent syneresis of the composition, especially after it becomes quiescent, e.g., upon placement in a blasting site. When sulfur is used, it may be in porportions of 0.5 to 5% and even up to 8 or 10% or more in some cases.

The use of these explosive compositions, as will be understood by those skilled in the art, may and often will require the choice and use of special and appropriate boosters and detonators, depending on the particular use as well as the particular composition. In particular, the booster should have high brisance or high-pressure characteristics.

It will be obvious that other materials also may be included. Explosive materials, including nitrated organic materials, nitrocellulose (smokeless powder), picric acid, and many other known and widely used high explosives and propellants may be included as auxiliary sensitizers or to add blasting power. The invention contemplates use of all such materials and such other unnamed and obvious variations, alternatives, expedients and modifications as will occur to those skilled in the art. It is intended to cover all such in the claims which follow, as far as the prior art properly permits.

What is claimed is:

1. A slurry type blasting composition which comprises, in combination, a major proportion of an inorganic nitrate selected from the group which consists of sodium nitrate, ammonium nitrate, and mixtures thereof, a suitable proportion of water and a thickener therefor to form a plastic gel or slurry including a sensitizing quantity not exceeding 5% by weight, based on the total composition of finely divided aluminum having a surface area of at least 0.5 square meter per gram and a lyophobic surface capable of forming void reaction sites, and a fuel other than said finely divided aluminum in sufficient proportions to bring oxygen balance Within limits of il%.

2. Composition according to claim 1 wherein ammonium nitrate comprises more than half the total inorganic nitrate.

3. Composition according to claim 1 wherein ammonium nitrate comprises more than 65% by weight of the total inorganic nitrate.

4. Composition according to claim 1 wherein the aluminum content is between about 0.05 and 5% by weight. I

5. Composition according to claim 1 wherein the aluminum has a surface area of at least one square meter per gram and is present in proportions of at least 0.05% by weight.

6. Composition according to claim 1 wherein the aluminum comprises at least 0.05% by weight of stearic acid coated paint grade aluminum.

7. Composition according to claim 1 which also contains a small amount, of the same general order as the aluminum content, of a phosphorus containing inhibitor to oppose premature reaction between the aluminum and the water.

8. A blasting composition in the form of an aqueous gel or slurry comprising about 40 to 87.5% by weight inorganic nitrate of which a major part is ammonium nitrate, 8 to 25% water, a thickener for said water in proportions sufficient to substantially prevent extraction or intrusion by extraneous water, 0.05 to 5% of finely divided aluminum having a surface area of at least 0.5 square meter per gram and having wet-resistant property sutficient to establish multitudinous reaction centers throughout the composition, and a fuel other than the finely divided aluminum in sufficient proportions to bring oxygen balance within limits of 210%, the total proportions of water and aluminum being at least about 10 percent by weight of the total composition.

9. Composition according to claim 8 in which the fuel comprises 10 to by weight of molasses, the water content of said molasses being included within the limits of total water and aluminum.

10. Composition according to claim :8 wherein there is incorporated a thickening agent capable of inhibiting syneresis of the gel or slurry after it becomes quiescent.

11. Composition according to claim 10 wherein the thickening agent comprises 02 to 2% by weight of guar gum.

12. Composition according to claim 10 wherein the thickening agent comprises a starch.

13. Composition according to claim 12 wherein the thickening agent comprises a precooked starch.

14. Composition according to claim 8 which includes 5 to 20% by weight of sodium nitrate, the proportions of ammonium nitrate being reduced correspondingly.

15. A plastic blasting composition comprising an aqueous solution of an inorganic nitrate at least half of 20 which is ammonium nitrate, an additional amount of an inorganic nitrate above and beyond that in solution, a sensitizing amount of finely divided particulate aluminum having surface active properties for establishing void reaction sites and a surface area of at least: 0.5 square meter per gram, a fuel other than said aluminum in proportions to bring oxygen balance within :10%, and a slurry thickener, the amount of water being at least 7% by weight of the total composition, and the total aluminum and water constituing about 10 to over 15% of the total.

16. Composition according to claim 15 which contains about 0.5 to 10% by weight of sulfur.

17. Composition according to claim 15 which contains 0.02 to 2% by weight of an inorganic phosphate inhibitor to reduce chemical activity between the aluminum and the water during storage.

References Cited UNITED STATES PATENTS 2,836,484 5/1958 Streng et al. 149-114 X 2,890,108 -6/1959 Toulmin 1491l4 X 2,935,394 5/1960 Hiler 1491l4 X 3,113,059 12/1963 Ursenbach et al 149-42 X 3,249,474 5/1966 Clay et a1. 149-41 X CARL D. QUARFORTH, Primary Examiner.

BENJAMIN R. PADGETI, Examiner. S. J. LECHERT, 111., Assistant Examiner. 

1. A SLURRY TYPE BLASTING COMPOSITION WHICH COMPRISES, IN COMBINATION, A MAJOR PROPORTION OF AN INORGANIC NITRATE SELECTED FROM THE GROUP WHICH CONSISTS OF SODIUM NITRATE, AMMONIUM NITRATE, AND MIXTURES THEREOF, A SUITABLE PROPORTION OF WATER AND A THICKENER THEREFOR TO FORM A PLASTIC GEL OR SLURRY INCLUDING A SENSITIZING QUANTITY NOT EXCEEDING 5% BY WEIGHT, BASED ON THE TOTAL COMPOSITION OF FINELY DIVIDED ALUMINUM HAVING A SURFACE AREA OF AT LEAST 0.5 SQUARE METER PER GRAM AND A LYOPHOBIC SURFACE CAPABLE OF FORMING VOID REACTION SITES, AND A FUEL OTHER THAN SAID FINELY DIVIDED ALUMINUM IN SUFFICIENT PROPORTIONS TO BRING OXYGEN BALANCE WITHIN LIMITS OF $10%.
 6. COMPOSITION ACCORDING TO CLAIM 1 WHEREIN THE ALUMINUM COMPRISES AT LEAST 0.05% BY WEIGHT OF STEARIC ACID COATED PAINT GRADE ALUMINUM. 